Liquid crystals may include liquids in which an ordered arrangement of molecules exists. Typically, liquid crystal (LC) molecules may be anisotropic, having either an elongated (rod-like) or flat (disk-like) shape. As a consequence of the ordering of the anisotropic molecules, a bulk LC often exhibits anisotropy in its physical properties, such as anisotropy in its mechanical, electrical, magnetic, and/or optical properties.
As a result of the rod-like or disk-like nature, the distribution of the orientation of LC molecules may play an important role in optical applications, such as in liquid crystal displays (LCDs). In these applications, LC alignment may be dictated by an alignment surface. The alignment surface may be treated so that the LC aligns relative to the surface in a predictable and controllable way. In many cases, the alignment surface may ensure a single domain through the LC device. In the absence of a treated alignment surface, the LC may have many domains and/or many discontinuities in orientation. In optical applications, these domains and discontinuities may cause scattering of light, leading to a degradation in the performance of the display.
Polarization gratings may be used to periodically affect the local polarization state of light traveling therethrough (as opposed to affecting the phase or amplitude as in some conventional gratings). For example, switchable liquid crystal polarization gratings (LCPGs) can be used to implement an intensity modulator that can operate on unpolarized light. While such polarization gratings have been fabricated to provide relatively high contrast for transmissive substrates, they may be difficult to implement on reflective substrates. In particular, switchable polarization grating designs may be difficult to create on reflective substrates, such as silicon (Si), aluminum (Al), gold (Au), and/or others, because the photo-alignment layers (which may be important to operation of the display) may be significantly corrupted by the reflection of the holographic ultraviolet (UV) beams used to pattern the photo-alignment layers from the reflective substrate. For example, when two orthogonally polarized holographic beams are incident on a reflective substrate, a strong reflection may occur to produce two additional beams in the opposite direction, which may result in interference and thus unwanted intensity variation in a direction normal to the substrate surface. Accordingly, the use of known fabrication techniques for transmissive substrates in the fabrication of reflective substrates may result in display devices having poor liquid crystal alignment, and thus, poor contrast.